1. Field of the Invention
The present invention relates to an image processing technique in an image reading apparatus, and particularly to an adaptation technique for image processing that is carried out in accordance with the image type on an original.
2. Description of the Related Art
Traditionally, in an image reading apparatus capable of reading a color image, a three-line CCD sensor formed by three lines including a red line sensor, a green line sensor and a blue line sensor is generally employed. The three-line CCD sensor has a configuration in which three one-dimensional line sensors are arrayed, having red, green and blue color filters arranged on their respective light receiving surfaces.
Also, in addition to the three-line CCD sensor provided in the traditional image reading apparatus, a four-line CCD sensor having a four-line configuration for reading a monochrome image has recently been disclosed, in which a monochrome reading line sensor with no color filter arranged on its light receiving surface is additionally provided.
In a traditional image reading apparatus having the four-line CCD sensor, the reading resolution of the monochrome reading line sensor is set to be higher than the reading resolution of the color reading line sensors. Thus, a low-resolution image read by the color line sensors can be converted to high resolution by using high-resolution image data read by the monochrome line sensor.
Originals from which images are to be read in the image reading apparatus are roughly classified into character images and line drawing images for which luminance resolution should be given priority, and photographic images for which color reproducibility should be given priority.
In the traditional image reading apparatus having the four-line CCD line sensor, in the case of converting the resolution of an image read by the color line sensors with an image read by the monochrome sensor, the resolution of the color image can be raised, but it may cause adverse effects (for example, color imbalance or the like) on the color reproducibility such as color balance of the color image data.
Such effects on the color reproducibility should be restrained to the minimum in the case of an image for which color reproducibility is emphasized, like a photographic image. The use of image processing must be properly distinguished in accordance with the image type of the original.